In the prior art, various compact and closed press sections are known in which there is a combination of press rolls which form at least three press nips with one another. Such prior art press sections include the applicant's "Sym-Press II" press section and "Sym-Press O" press section (trademarks of Valmet Paper Machinery, Inc.).
In the "Sym-Press II", the press section, the first twin-felt nip is formed between a hollow-faced lower press roll and an upper press-section roll, a suction roll forming the second nip with a smooth-faced center roll of the press, in connection with which center roll a third press nip is further formed.
In a "Sym-Press O" the press section, the first twin-felt horizontal nip is formed between a lower hollow-faced roll and an upper press-section press-section roll, whereupon the web follows the upper fabric as a vertical run into the second nip. The second nip is formed between a hollow-faced press roll, separate from the rolls of the first nip, and a smooth-faced centre roll. A third press nip, provided with a felt, is further formed in connection with said centre roll with a hollow-faced press roll.
In compact press sections, the replacement of rolls and press fabrics is problematic. To solve these problems, the applicant has developed a "QF" press frame (trademark of Valmet Paper Machinery, Inc.) which is disclosed in applicant's published FI patent application Nos. 70,951 and 73,025, as well as in U.S. Pat. Nos. 4,608,125 and 4,699,692. As condensed, in a QF frame, the space placed between the front and rear frame parts and above the press-roll combination has been arranged open or openable so that the upper fabrics and at least the upper press rolls can be replaced quickly and easily by making use of the open or openable space.
In the prior art, "Sym-Press O" press section of the applicant, the hollow-faced press roll of the second nip is supported on a beam construction, which is provided with two L-shaped arms. The lower part of this beam construction is linked in connection with the front frame of the press, and its opposite end is attached, by means of openable joints, in connection with the bearing supports of the center roll of the press. Upon opening the joints, the beam construction can be pivoted to the open position when the first upper fabric and the press rolls are being replaced. The beam construction is arranged to be opened and closed by means of a pair of hydraulic cylinders. A second set of support arms is linked with the beam construction. The hollow-faced press roll of the second nip is mounted on the second set of support arms. The second set of support arms are loaded by means of a particular pair of hydraulic cylinders, by whose means the linear load in the second nip against the center roll is produced. The center roll is mounted on fixed supports.
In the prior art construction for loading and opening of a press roll described above, there are two pairs of arms placed one inside the other as well as two pairs of hydraulic actuators, one for opening of the construction and the other one for loading of the nip. Moreover, underneath the press roll the second nip, there is a separate splash plate, which protects the upper press roll from splashes coming from the suction roll placed underneath. This splash plate must be lifted out of its place of operation separately in connection with replacement of roll.
The prior art support construction described above is mechanically complicated and expensive, and it includes a great number of articulated joints and hydraulic actuators. Also, the support construction is susceptible of vibrations. In the support construction, replacement of the lower and upper felts of the first nip is quite complicated, because four separate disassembling operations are required in connection with the replacement of two felts. This increases the costly standstill time required for replacement of felts.